Single map set in a marble citadel, for Boom+.
The gimmick here is that all the monsters are spectral, be advised.
Gameplay: Single player.
Build time: 20 hours.
Difficulty settings: Yes.
Credits: Textures are from cc4-tex, sky from Mechadon's Box o skies.
Download

@StormCatcher.77
Cool, thanks for the review.
Well, the pedestal is at the very center of the map, with switches on all sides, so I figured the player would spot it at some point. I'll highlight the switches a bit more.
@Spectre01
The central area lags for me too. I only have a 5-year-old laptop though.

Yep.
And there's also Khorus's WIP project for Strife with the same name... But I don't think all these wads will get confused with one another, they're all different.
There are a couple more Eternity exclusives out there. Vaporware is a must play for sure.

So I never cared much for Eternity, portals or any features beyond Boom until one day I randomly came across a test map which showcased portals. I opened it in the editor, thought, "Well, that's not too difficult, what if..." One thing led to another, and several months later:
This is a single map for the latest (4.00.00) version of Eternity.
Gameplay: Single player.
Build time: 100 hours.
Difficulty settings: Yes.
Freelook: Not needed, but allowed.
Credits: skillsaw and the authors of aa-tex.wad; stewboy for the midi.
Issues: Possible performance drops. Sorry.
Downloads:
Mothership
Eternity v 4.00.00
(You don't need aa-tex to play this)